In recent years many plug-in electric vehicles have been introduced into the market. These electric vehicles can be either fully electric vehicles or hybrid electric vehicles. These vehicles run on electrical energy stored in a battery. Electric vehicle owners typically charge the battery in their homes and garages using a charging outlet connected to the main electrical supply from the utility to the home.
Electric vehicles draw a major amount of power from the power grid at around 7.2 KW and take about 6-8 hours to charge completely. The current draw for the chargers is about 30 Amps at 240 Volts. Such amounts of power draw create a heavy load on transformers and other electric power delivery grid infrastructure installed by utilities. Utilities typically install a single transformer for every 4-6 houses in a neighborhood. If two or more people in the houses connected to a transformer charge their electric vehicles at the same time, degradation or even failure of the transformer may occur. Failure or degradation of a transformer can result in loss of electricity for all the households. These failures will be even more pronounced in case of variable pricing for the electrical energy. When electricity prices go down based on the time of the day, for example at 9 PM, owners of electric vehicles may all want to start charging their vehicles at the same time to take advantage of the reduced price.